I made a Trifield decoder a few months ago (with the help of Aaron
Heller, to understand how to use Faust), and it works surprisingly
well! The distances can be adjusted, so it would work with 3 speakers
on a plane. The only problem is the patent... So I'm not sure I can
distribute it.

--
Marc

Tue, 8 Apr 2014 20:00:57 +0200,
JQ Adams <jqad...@google.com> wrote :

> Trifield is new to me.  Thanks for this.
> 
> I'm not entirely certain what is said in this article...:
> 
> *Each filtered signal then passes to a sine/cosine potential divider,
> which
> > is set differently for each frequency band. Only with this
> > arrangement, Gerzon found, could a wide stereo image and sharpened
> > central focus be traded off effectively against one another across
> > the entire audible spectrum.[image: Inline image 1]*
> 
> 
> This seems to be saying that different weightings of energy gets sent
> to the middle versus side speakers.  I would presume the center
> channel would receive the greater proportion of low frequency
> content, but it's not said here, directly.
> 
> Funny enough, I did have in mind to ask in followup whether the the
> L/R speakers could effectively be just small tweeters, as my
> understanding is for a person to decode direction, it's most
> important that high frequency energy is reproduced well.  Practically
> (for me) it simplifies/reduces cost/is more discreet to have small
> drivers added to the sides of monitors. I had not thought about a
> need to reduce the high frequency energy to the center channel...but
> in a way that sorta sounds reasonable...
> 
> One further question I would pose is that of necessity of delays.  In
> my instantiation, the loudspeakers would all be on a plane (the front
> wall), and thus for a centered listening position, the center
> loudspeaker would be closer.  Given that we may have a dual video
> screen system, the perceived angle may be upwards of 90° for a
> near-seated participant.  Imagining this as a 45-45-90 right triangle
> with the listener at the right angle, the loudspeakers would be on
> the hypotenuse at distances of *s*, sqrt(2)/2**s*, *s* for left,
> center, right.  This would seem to indicate a delay on the center
> channel that scales in magnitude with the size of the room.  When *s*
> is 3m, the distance variance would be about .88m, or about 2.5ms,
> which I don't know whether is significant...
> 
> 
> On Tue, Apr 8, 2014 at 7:06 PM, Paul Hodges
> <pwh-surro...@cassland.org>wrote:
> 
> > --On 08 April 2014 18:45 +0200 JQ Adams <jqad...@google.com> wrote:
> >
> > > My question pertains to play back to a three speaker setup (left,
> > > center, right)...would it be most correct to send the 'mid' signal
> > > directly to a center speaker and the 'side' signal to speakers
> > > left and right, phase inverted from each other?
> >
> > Have you thought of Trifield as a possibility?
> >
> > <
> > http://www.stereophile.com/content/upward-mobility-2-channels-surround-page-2
> > >
> >
> > Paul
> >
> > --
> > Paul Hodges
> >
> >
> > _______________________________________________
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